PIC16CE62X
Note: On reset, the TRISA register is set to all
inputs. The digital inputs are disabled and
the comparator inputs are forced to ground
to reduce excess current consumption.
5.0
I/O PORTS
The PIC16CE62X parts have two ports, PORTA and
PORTB. Some pins for these I/O ports are multiplexed
with an alternate function for the peripheral features on
the device. In general, when a peripheral is enabled,
that pin may not be used as a general purpose I/O pin.
TRISA controls the direction of the RA pins, even when
they are being used as comparator inputs. The user
must make sure to keep the pins configured as inputs
when using them as comparator inputs.
5.1
PORTA and TRISA Registers
The RA2 pin will also function as the output for the
voltage reference.When in this mode, the VREF pin is a
very high impedance output. The user must configure
TRISA<2> bit as an input and use high impedance
loads.
PORTA is a 5-bit wide latch.RA4 is a SchmittTrigger input
and an open drain output.Port RA4 is multiplexed with the
T0CKI clock input. All other RA port pins have Schmitt
Trigger input levels and full CMOS output drivers. All pins
have data direction bits (TRIS registers) which can config-
ure these pins as input or output.
In one of the comparator modes defined by the
CMCON register, pins RA3 and RA4 become outputs
of the comparators. The TRISA<4:3> bits must be
cleared to enable outputs to use this function.
A '1' in the TRISA register puts the corresponding output
driver in a hi- impedance mode. A '0' in the TRISA register
puts the contents of the output latch on the selected pin(s).
Reading the PORTA register reads the status of the pins
whereas writing to it will write to the port latch. All write
operations are read-modify-write operations. So a write
to a port implies that the port pins are first read, then this
value is modified and written to the port data latch.
EXAMPLE 5-1: INITIALIZING PORTA
CLRF PORTA
;Initialize PORTA by setting
;output data latches
;Turn comparators off and
;enable pins for I/O
;functions
MOVLW 0X07
MOVWF CMCON
The PORTA pins are multiplexed with comparator and
voltage reference functions. The operation of these
pins are selected by control bits in the CMCON
(comparator control register) register and the VRCON
(voltage reference control register) register. When
selected as a comparator input, these pins will read
as '0's.
BSF
STATUS, RP0 ;Select Bank1
MOVLW 0x1F
;Value used to initialize
;data direction
MOVWF TRISA
;Set RA<4:0> as inputs
;TRISA<7:5> are always
;read as '0'.
FIGURE 5-2: BLOCK DIAGRAM OF RA2 PIN
Data
FIGURE 5-1: BLOCK DIAGRAM OF
RA1:RA0 PINS
bus
D
Q
Q
Data
VDD
P
WR
PortA
bus
D
Q
Q
CK
VDD
P
WR
PortA
Data Latch
CK
D
Q
Data Latch
RA2 Pin
N
WR
TRISA
D
Q
Q
CK
I/O Pin
N
WR
TRISA
VSS
TRIS Latch
CK
Q
Analog
Input Mode
VSS
TRIS Latch
Analog
Schmitt Trigger
Input Buffer
Input Mode
RD TRISA
Schmitt Trigger
Input Buffer
RD TRISA
Q
D
Q
D
EN
EN
RD PORTA
RD PORTA
To Comparator
VROE
To Comparator
VREF
Note: I/O pins have protection diodes to VDD and VSS.
Note: I/O pins have protection diodes to VDD and VSS.
1998 Microchip Technology Inc.
Preliminary
DS40182A-page 23
MICROCHIP [ MICROCHIP ]
